1. Field of the Invention
The present invention relates to the overall architecture of a video monitor and, more particularly, to its gain control assembly.
2. Description of the Prior Art
FIG. 1 schematically shows the conventional overall architecture of a video monitor and, more particularly, of the components designed to control the gain of the input video signal. As shown, the video monitor of FIG. 1 comprises a cathode-ray tube 1, a screen 2 which corresponds to the front face of the video monitor, and a socket 3 which is arranged at the rear face of the video monitor. For ergonomic and aesthetical reasons, it is generally desired to position all the control buttons of the video monitor on its front face and all the input and output signal connectors on its rear face. Thus, a cable 5 leading a video signal to a connector 6 is arranged on the monitor rear face, and this video signal is then routed towards the front face for adjustment by a potentiometer 8 set by a control button 9 and then routed back towards the rear face to a circuit 10 for amplifying and processing of the video signal. Circuit 10 is preferably arranged close to the tube socket 3.
Since the video signal is a high frequency signal, the spectrum of which is liable to have a value of about a hundred MHz, it is necessary to take steps to avoid parasitic radiations. Thus, between the connector 6 and potentiometer 8, a first portion of coaxial cable 11 is generally provided, while between this potentiometer 8 and circuit 10 a second portion of coaxial cable 12 is also provided. For a monitor screen 2 having a diagonal width of about 30 cm (12 inches), the monitor depth will be on the order of a few tens of centimeters. However, using a couple of relatively rigid coaxial cables having a length of several tens of centimeters causes several drawbacks:
they are not easy to connect, which results in high manufacturing cost; PA1 they are fragile, which adversely affects quality; PA1 they are liable to generate a relatively high electromagnetic radiation, especially at their terminations; and PA1 they have to be connected to adapted impedances, which makes it compulsory, for example, for the potentiometer to provide for an intermediate impedance adaptation stage.
Despite those drawbacks, such coaxial cables are provided on practically all monitors for which it is desired to keep the control buttons on the front face.